In one conventional practice called vacuum arc remelt (VAR), titanium alloys are prepared by furnishing the starting metallic materials in the form of virgin metal, revert metal, scrap, and the like. These starting metallic materials are cut into smaller pieces as necessary, and welded together to form an elongated, irregularly shaped consumable electrode. The consumable electrode is loaded into a vacuum arc melting furnace, and a vacuum is drawn. An electrical arc is struck between the vertically oriented consumable electrode and the interior of a crucible, while under vacuum. The arc melts the end of the electrode, and the molten metal falls into the crucible to form a molten pool. In the case of a cold-crucible melting technique, the arc is continued, and the electrode is gradually fed into the crucible as the metal is progressively melted from the end of the electrode at which the arc is struck and solidifies progressively during melting. If the melted metal is to be cast, when the volume of metal in the crucible is sufficient, it is cast into a mold and solidified. The casting may serve as a final product or as a remelt material, because there may be multiple remelts of the metal to achieve sufficient homogeneity. There are other melting technologies, but most use a consumable electrode during the early stages of melting, and in each case the consumable electrode is prepared by welding the starting metallic materials together.
This type of approach, while widely practiced, has some significant shortcomings and limitations. The cutting and welding of the starting metallic materials are labor intensive and expensive. There is a wide variety in the form and chemistry of the starting metallic materials. The chemistry of the consumable electrode varies greatly over its length, so that the composition of the metal being melted at any moment locally varies greatly as the consumable electrode is fed into the molten pool. There may also be impurity pickup during handling and welding of the consumable electrode. Debris may accumulate in the relatively large surface crevices and be carried into the melt. Mechanical and chemical irregularities present in the starting metallic material may not be eliminated during the melting operation, so that the final product has at least a remnant of the irregularities.
The welding of the starting metallic materials into the irregular but generally rodlike form of the consumable electrode must be performed with great care. The weld may have associated irregularities, such as oxide particles if the welding is performed in air. If a transverse weld joint is understrength, the entire end of the consumable electrode below the weld joint may drop off into the molten pool, interrupting the melting operation and possibly damaging the melting equipment. And even if the transverse welds are sound, they have an associated electrical resistance such that the electrical current flowing through the consumable electrode may cause one of the welds to heat and fail, again causing all of the consumable electrode below the failed weld to fall into the molten pool.
In yet other cases, there is simply no way to manufacture a rod of some materials in a form suitable for use as a consumable electrode.
There is a need for an improved approach to the fabrication of consumable electrodes. Many of the same problems are also observed in other types of elongated rodlike structures. The present approach provides a solution to the problems associated with the present technology, and further provides related advantages.